The globe artichoke is a perennial variety of a thistle native to the Mediterranean region that is cultivated as a food. The edible portion of the plant consists of the flower buds before the flowers come into bloom. Once the buds bloom the structure changes to a coarse, barely edible form. Artichokes are usually preserved in oil, vinegar or brine as cooked artichokes (particularly those that have been cut) can turn brown due to enzyme action and chlorophyll oxidation. In Italy, artichoke hearts in oil are the usual vegetable for "spring" section of the "Four Seasons" pizza.